Forward scanning optical probes are used in various applications, including imaging, diagnostic and surgical devices. Forward scanning optical probes, or for short, scanning probes, emit light at a distal end of the scanning probe and scan the emitted light across a target region. In imaging applications, these scanning probes also collect the light, reflected from the target region, and deliver the collected light to an imaging system.
The scanning probes utilize scanning mechanisms, examples of which include microelectromechanical scanners and piezoelectric scanners. However, implementing these scanning mechanisms within the narrow confines of a scanning probe for medical applications, such as within a cannula of a medical endoprobe with a diameter of less than 1 mm, proved to be particularly challenging.
The scanning can be performed along a one dimensional (1D) line, or along two dimensional (2D) patterns. One design to achieve a 2D scanning capability includes a “paired angle rotation scanning” (PARS) probe. Such PARS probes have been suggested, e.g., for Optical Coherence Tomography (OCT) imaging applications. A PARS probe utilizes a pair of angle-cut GRIN lenses, one rotated by an outer cannula and the other counter-rotated in the opposite direction by an inner cannula, housed within the outer cannula. The synchronized counter-rotation of the two GRIN lenses can deflect and scan an OCT probe beam along a variety of 2D scanning patterns in the target region ahead, or forward, of the probe tip. It proved to be possible to design PARS probes with an outer diameter of 1.65 mm. However, PARS designs have their own limitations, as follows.
1. The two counter-rotating cannulas of a PARS probe require challengingly high precision manufacturing.
2. Implementing some of the widely used scanning patterns can be another challenge. For example, to achieve a 1D linear scan, the two cannulas have to be counter-rotated at exactly the same angular velocity in opposite directions. Even a small difference, or mismatch, of the angular velocities disadvantageously results in a non-linear scan pattern, typically not even a closed loop.
Another example is the moving of the scanning beam to a specific point, e.g., to start a new scan. Doing so also requires that the two GRIN lenses are synchronously rotated by the same angle in opposite directions. If the rotations of the two GRIN lenses are not synchronized with high enough precision and end up moving the scanning beam to a shifted position, then the shift of the coordinates of the specific point needs to be compensated by a shift of the calibration of the imaging system.
Some systems attempt to improve the precision of the counter-rotation, but those systems typically introduce additional complexities into the already tight space of the probe.